1. Field of the Invention
This invention relates to magnetic bubble lattice file storage, and in particular to structures and techniques for providing reordering capability in such storage in order to improve the access time to information in the bubble lattice file. In turn, this improves the usefulness of the bubble lattice file, especially where such a file is of extremely large capacity.
2. Description of the Prior Art
Various storage systems using magnetic bubble domains are well known. For example, a first form of bubble domain storage uses magnetic elements comprised of magnetic overlays or ion implanted regions for moving bubble domains in response to the reorientation of an in-plane magnetic field. These are the well known field access devices which can be comprised of, for example, T and I bar elements for moving magnetic bubble domains. In this type of field access storage, several techniques are known for improving the access time to bubble domains in the storage and for reordering the data in accordance with data management needs. For instance, dynamically ordered magnetic bubble storage is described in U.S. Pat. No. 3,670,313. In that technique, data in a shift register is reordered in order of last use to reduce the average access time to data in the register. In the least recently used algorithm, the closeness of the data to the access position is in accordance with whether or not it has been recently used. This is based on the thought that data which has been requested is more likely to be requested again more soon than data which has not been previously requested.
Other forms of dynamically ordered storage including those implementing the least recently used algorithm are described in U.S. Pat. Nos. 3,704,452, 3,766,534 (multiple bit resorting using multiple access positions), and U.S. Pat. No. 3,797,002 (pages stored in memory are divided in two groups with the pages of one group being accessed at one end of the shift registers while the pages of the other group are accessed at the other end of the shift registers). In addition, U.S. Pat. No. 3,701,132 describes data reordering in a major/minor loop bubble storage device.
A second type of magnetic bubble domain storage is the magnetic bubble lattice file in which the bubble domains are packed so close to one another that they interact with one another. This type of storage provides extremely high density in contrast with the type of storage previously described and offers the promise of very high capacity, very high density store. Bubble lattice file storage is described more particularly in U.S. Pat. No. 4,052,710. The bubble lattice file was also described by O. Voegeli et al in a paper entitled "The Use of Bubble Lattices for Information Storage", appearing in the Proceedings of the 20th Annual Conference on Magnetism and Magnetic Materials, Dec. 3-6, 1974, at San Francisco, Calif. At that conference, other papers on various aspects of the bubble lattice file were also presented.
In the bubble lattice file, domains are customarily used to represent information in accordance with their wall magnetization properties. This type of coding is generally described in U.S. Pat. No. 3,890,605. The lattice is initialized by any of a variety of techniques, such as that described in U.S. Pat. No. 3,953,842. Bubble domains in the lattice are translated back and forth to access channels where columns of bubble domains can be removed for reading of information and for writing new information into the lattice. A technique for translating the lattice domains is described in U.S. Pat. No. 3,930,244, while the column access technique for removing columns of bubble domains is described in copending application Ser. No. 429,601, filed Jan. 1, 1974, now U.S. Pat. 4,040,038. A bubble domain pump for moving magnetic bubble domains in the access channel is described in U.S. Pat. No. 3,913,079. A technique for stabilizing information states in the bubble lattice file using capping layers is described in U.S. Pat. No. 3,930,243.
It is apparent that considerable progress has been made in the development of bubble lattice files and that components exist for writing information into these files, reading information from these files, translating the lattice bubble domains, and removing selected columns of bubble domains from the lattice for I/O operations. However, the relative location of data in the bubble lattice file is fixed and no simple way has been proposed to implement in this type of file the type of dynamic ordering which has been described with respect to conventional field access bubble devices. If the bubble lattice file is to be used for storing large data bases, it is necessary to provide a technique for dynamic ordering in order to facilitate fast access in such a file. Further, such reordering is necessary to improve the average access time to information in the lattice file and to thereby increase the usefulness of such a large capacity storage system.
Accordingly, it is a primary object of the present invention to provide a simplified structure and technique for reordering data in a magnetic bubble lattice file.
It is another object of this invention to provide techniques and structure for improving the average access time to data in a magnetic bubble lattice file.
It is a further object of this invention to provide techniques for increasing the usefulness of magnetic bubble lattice files, and more particularly that type of file which is of extremely large capacity.